Modern day radiotherapy has developed in complexity to the degree that significant treatment errors are both difficult to detect and difficut to completely avoid. In the current day radiotherapy department it is common to have a large number of patients being treated with Intensity Modulated Radiotherapy (IMRT) techniques. When treating patients with these techniques it can be difficult to detect patient setup errors and virtually impossible to detect beam collimation errors without the use of automated secondary checks. Incorrect dose delivery or dose delivered to the wrong area is also an ongoing treatment risk. Despite gains in the implementation of automated mechanisms for detection of errors the incidence of concerning treatment misadministrations is still significant. Treatment delivery errors in the modern era have been reported by several authors as occurring during from 1 to 2 % of patients' courses of treatment. While most of these are judged to not be of clinical importance, the rate of significant treatment errors is still thousands of incidents per yar in the United States alone. Compromised radiotherapy treatments can lead to lower control rates and/or higher complication rates. We will develop a system that will provide the radiotherapy clinic with the capability to completely and independently measure the geometric alignment and dosimetric compliance of an individual treatment fraction in real time as the patient is treated with any arbitrarily complex treatment technique. The system will consist of a high density cloak of radiation detectors deployed in a ring centered on the treatment apparatus isocenter and within the rotational circle of the head(s) of the radiation delivery system. The detector cloak will surround the area within the patient being treated and will measure the radiation fluence both entering and exiting the patient. The dosimetric data acquired at the time of treatment will allow for the calculation of the complete dose distribution actually delivered to the patient for each and every treatment session. The detection system will be physically and electronically independent of the treatment system thereby providing a truly comprehensive secondary monitor of the delivered dose. Development and clinical deployment of a completely independent treatment verification system for radiotherapy has the potential to significantly reduce radiotherapy treatment errors. The reduction of treatment delivery errors can increase local tumor control rates, reduce the rate of treatment complications or both. The ongoing compilation of actual treatment delivery compliance data will serve as invaluable confirmation of the benefit, or lack thereof, of newly implemented quality assurance techniques.